To add test_alarm_is_on_when_pressure_out_of_range() and test_alarm_i…

…s_off_when_pressure_within_range(), create customerized mock to isolate sensor, meanwhile, make sensor as public variable.

TDDMicroExercises/Ruby/tire_pressure_monitoring_system/alarm.rb

@@ -3,7 +3,7 @@
 class Alarm
 
   attr_reader :alarm_on
-
+  attr_accessor :sensor
   def initialize
     @sensor = Sensor.new
     @alarm_on = false

TDDMicroExercises/Ruby/tire_pressure_monitoring_system/test/alarm_test.rb

@@ -1,9 +1,39 @@
 require 'test/unit'
 require_relative '../alarm'
+require_relative '../sensor'
+
+class MockSensor < Sensor
+	def initialize psi_value
+		@psi_value = psi_value
+	end
+
+	def pop_next_pressure_psi_value
+		@psi_value
+	end
+end
 
 class AlarmTest < Test::Unit::TestCase
   def test_alarm_is_off_after_it_initialized
     alarm = Alarm.new
     assert_equal false, alarm.alarm_on
   end
+
+  def test_alarm_is_on_when_pressure_out_of_range
+    alarm = Alarm.new
+    alarm.sensor = MockSensor.new(10)
+
+    alarm.check
+
+    assert_equal true, alarm.alarm_on  	
+  end
+
+  def test_alarm_is_off_when_pressure_within_range
+    alarm = Alarm.new
+    alarm.sensor = MockSensor.new(20)
+
+    alarm.check
+
+    assert_equal false, alarm.alarm_on  	
+  end
+
 end